The automatic hold function AVH (Automatic Vehicle Hold) is a supplementary braking function which assists the operator to hold the vehicle stationary. In that process the vehicle is braked automatically (i.e., without any need for the operator to press the brake pedal), until the operator presses the accelerator pedal again. The AVH function normally goes into action when the operator brakes the vehicle to a standstill, but it also acts in cases when the vehicle rolls to a standstill. Here, a critical point is detection that the vehicle has reached a standstill.
From the related art it is known that the stationary state of a vehicle can be detected through evaluation of information from wheel speed sensors. Conventional wheel speed sensors, however, have the disadvantage of providing a very inaccurate measurement signal at very low vehicle speeds, for example under 3 km/h. In addition, the measuring method (Hall effect sensor having a sensor wheel) of the wheel speed sensors commonly used causes the latter, rather than measuring the present vehicle speed, to measure a speed that is already in the past. As a result, the true present vehicle speed is generally not the same as the measured vehicle speed. The stationary state of the vehicle can thus not be determined with sufficient accuracy. In particular where the vehicle is rolling to a standstill uphill, the result may be that the automatic hold function is activated only when the vehicle is already rolling back down again. This is irritating and inconvenient for the operator. On the other hand, if the automatic hold function is activated permaturely, the vehicle is braked harshly.
Consequently, an object of the present invention is to determine the optimum moment for activation of the automatic hold function, namely when the vehicle reaches a standstill, as accurately as possible.